1. Field of the Invention
The present invention relates to an electrostatic chuck device, and more particularly, to an electrostatic chuck device suitable for use in a high-frequency discharge type plasma processing apparatus for applying a high-frequency voltage to an electrode to generate plasma and processing a plate-like sample such as a semiconductor wafer, a metal wafer, and a glass plate by the use of the generated plasma.
Priority is claimed on Japanese Application No. 2006-218446, filed Aug. 10, 2006, which is incorporated herein by reference. This application also claims the benefit pursuant to 35 U.S.C. §102(e) of U.S. Provisional Application No. 60/828,407, filed on Oct. 6, 2006.
2. Description of the Related Art
Conventionally, plasma was often used in processes such as etching, deposition, oxidation, and sputtering for manufacturing semiconductor devices such as IC, LSI, and VLSI or flat panel displays (FPD) such as a liquid crystal display, in order to allow a process gas to react sufficiently at a relatively low temperature. In general, methods of generating plasma in plasma processing apparatuses are roughly classified into a method using glow discharge or high-frequency discharge and a method using microwaves.
FIG. 11 is a cross-sectional view illustrating an example of an electrostatic chuck device 1 mounted on a known high-frequency discharge type plasma processing apparatus. The electrostatic chuck device 1 is disposed in a lower portion of a chamber (not shown) also serving as a vacuum vessel and includes an electrostatic chuck section 2 and a metal base section 3 fixed to the bottom surface of the electrostatic chuck section 2 so as to be incorporated into a body.
The electrostatic chuck section 2 includes: a substrate 4, which has a top surface serving as a mounting surface 4a, on which a plate-like sample W such as a semiconductor wafer is disposed, so as to adsorb the plate-like sample W in an electrostatic manner, and an electrostatic-adsorption inner electrode 5 built therein; and a power supply terminal 6 for applying a DC voltage to the electrostatic-adsorption inner electrode 5. A high DC voltage source 7 is connected to the power supply terminal 6. The metal base section 3, which is also used as a high-frequency generating electrode (lower electrode), is connected to a high-frequency voltage generating source 8 and has a flow passage 9 for circulating a cooling medium such as water or an organic solvent formed therein. The chamber is grounded.
The electrostatic chuck device 1 adsorbs the plate-like sample W, by placing the plate-like sample W on the mounting surface 4a and allowing the high DC voltage source 7 to apply a DC voltage to the electrostatic-adsorption inner electrode 5 through the power supply terminal 6. Subsequently, a vacuum is formed in the chamber and a process gas is introduced thereto. Then, by allowing the high-frequency voltage generating source 8 to apply high-frequency power across the metal base section 3 (lower electrode) and an upper electrode (not shown), a high-frequency electric field is generated in the chamber. Frequencies of several tens of MHz or less are generally used as the high frequency.
The high-frequency electric field accelerates electrons, plasma is generated due to ionization by collision of the electrons with the process gas, and a variety of processes can be performed by the use of the generated plasma.
In the recent plasma processes, there is an increased need for processes using “low-energy and high-density plasma” having low ion energy and high electron density. In the processes using the low-energy and high-density plasma, the frequency of the high-frequency power for generating plasma might increase greatly, for example, to 100 MHz.
In this way, when the frequency of the power to be applied increases, the electric field strength tends to increase in a region corresponding to the center of the electrostatic chuck section 2, that is, the center of the plate-like sample W, and to decrease in the peripheral region thereof. Accordingly, when the distribution of the electric field strength is not even, the electron density of the generated plasma is not even and thus the processing rate varies depending on in-plane positions of the plate-like sample W. Therefore, there is a problem in that it is not possible to obtain a processing result excellent in in-plane uniformity.
A plasma processing apparatus shown in FIG. 12 has been suggested to solve such a problem (see Patent Literature 1).
In the plasma processing apparatus 11, in order to improve the in-plane uniformity of the plasma process, a dielectric layer 14 made of ceramics or the like is buried at the central portion on the surface of the lower electrode (metal base section) 12 supplied with the high-frequency power and opposed to the upper electrode 13, thereby making the distribution of the electric field strength even. In the figure, reference numeral 15 denotes a high frequency generating power source, PZ denotes plasma, E denotes electric field strength, and W denotes the plate-like sample.
In the plasma processing apparatus 11, when the high frequency generating power source 15 applies the high-frequency power to the lower electrode 12, high-frequency current having been transmitted on the surface of the lower electrode 12 and having reached the top due to a skin effect flows toward the center along the surface of the plate-like sample W, and a part thereof leaks toward the lower electrode 12 and then flows outward inside the lower electrode 12. In this course, the high-frequency current is submerged deeper in the region provided with the dielectric layer 14 than the region not provided with the dielectric layer 14, thereby generating hollow cylindrical resonance of a TM mode. As a result, the electric field strength at the center supplied to the plasma from the surface of the plate-like sample W is weakened and thus the in-plane electric field of the plate-like sample W is made to be uniform.
The plasma process is often performed under depressurized conditions close to a vacuum. In this case, an electrostatic chuck device shown in FIG. 13 is often used to fix the plate-like sample W.
The electrostatic chuck device 16 has a structure such that a conductive electrostatic-adsorption inner electrode 18 is built in a dielectric layer 17. For example, the conductive electrostatic inner electrode is interposed between two dielectric layers formed by thermally spraying alumina or the like.
The electrostatic chuck device 16 adsorbs and fixes the plate-like sample W by the use of the electrostatic adsorption force generated on the surface of the dielectric layer 17 by allowing the high DC voltage source 7 to apply the high DC power to the electrostatic-adsorption inner electrode 18.
[Patent Literature 1] Japanese Patent Unexamined Publication No. 2004-363552 (see paragraphs 0084 and 0085 of page 15 and FIG. 19)
In the known plasma processing apparatus 11 described above, when the electrostatic chuck device 16 processes the plate-like sample W by the use of the plasma in a state where it is disposed on the lower electrode 12, the high-frequency current does not pass through the electrostatic-adsorption inner electrode 18 of the electrostatic chuck device 16 and thus a flow of current directed to the outside from the electrostatic-adsorption inner electrode 18 is generated.
In other words, since the electrostatic-adsorption inner electrode 18 is disposed in the electrostatic chuck device 16, the dielectric layer 14 is not viewed from the plasma PZ and thus an effect of lowering the potential of the plasma in the region in which the dielectric layer 14 is buried cannot be exhibited.
As a result, the potential of the plasma above the central portion of the plate-like sample W is high and the potential above the peripheral portion is low, thereby making the processing rate different between the central portion and the peripheral portion of the plate-like sample W. Accordingly, this is a reason for in-plane unevenness of the plasma process such as etching.